The invention relates to a pneumatic brake system, and in particular to a device permitting continued brake operability and compressed air flow control in the event of a system emergency such as a rupture in a pneumatic supply line.
Vehicles, particularly commercial vehicles such as trucks and buses, typically have pneumatic braking systems. These pneumatic brake systems typically include air-operated actuators for applying disc brakes or drum brakes at the wheels of the vehicle. The air-operated actuators (also known as spring brake actuators due to their being provided with a powerful spring which automatically applies the brake when pneumatic pressure to the actuator is lost) are supplied with compressed air to their service brake-operating portions by networks of pneumatic air lines and hoses. The air lines are typically controlled via relay valves which control the distribution of compressed air to the various brakes in response to pneumatic and/or electrical control signals delivered from a driver brake actuating device (such as a brake pedal) and/or an electronic controller (such as an anti-lock braking system controller).
There is a wide variety of known arrangements for compressed air brake actuation distribution in various commercial vehicles, with individual vehicle pneumatic line arrangements adapted as desired to the particular type of vehicle and the design objectives of the system. For example, a commercial vehicle having separate tractor and trailer units typically has separate readily-disconnectable brake line circuits dedicated to control of the trailer's brakes, and a dedicated pneumatic circuit for the tractor's brakes. Other commercial vehicles such as so-called “straight” (e.g., box trucks with all wheels mounted on a single frame) trucks and “bobtail” tractors (e.g., “4×2” vehicles with one front axle and one rear axle) may have separate pneumatic circuits for the front and rear axle brakes.
One variation on pneumatic brake systems is the so-called “dual air system” front brake arrangement, in which braking air may be supplied from front and/or rear brake circuits to operate the brakes.
There are proposals to establish new stopping distance requirements in Federal Motor Vehicle Safety Standard, FMVSS 121, including a shortened requirement for stopping distance in the event of failed front brakes (i.e., and emergency braking event) on dual air brake systems of straight trucks and 4×2 trucks. The new stopping distance requirements are particularly challenging to meet, as they require the vehicle to be unloaded (empty), a condition which minimizes the load over the rear wheels and thus does not permit the rear brakes to generate a significant amount of emergency braking force.
This and other objectives are addressed by the present invention, which provides an approach to meeting the emergency braking requirements in a manner intended to address the requirements while avoiding excessive system complication and additional system production and maintenance costs.
In one embodiment of the present invention, a valve device is provided between the pneumatic lines serving the front air brakes and the lines servicing the rear brakes. The valve device may for example be located on an engine compartment firewall or other bulkhead
The valve device would permit rear brake compressed air to be provided to the front brakes in the event of an emergency braking event via an orificed air supply. A front brake system failure may include failures which block or prevent flow in the front brake compressed air supply circuit (such as a failure which prevents an air supply relay valve from opening) or a rupture of a circuit supply line. In the event of the latter, an orifice is provided in the valve device to avoid massive air loss from both the primary and secondary compressed air supplies. The valve device may also be configured to provide a biased differential pressure to the front brakes that is lower than the normal brake control pressure to prevent increased air system timing which would be necessitated if both braking systems were directly plumbed to the front brake actuators.
This two-way valve device may be in the form of a biased-orificed double check valve. In such an arrangement, the biased orifice prevents air flow from the rear pneumatic brake circuit to the front brake circuit during normal system operation (i.e., in the absence of a failure condition in the front brake circuit). During a front brake failure event, the biased-orificed double check valve would permit front brake application using rear brake circuit compressed air, while also slowing the loss of air from the rear brake circuit during the front brake failure event, and ensuring a high level of air flow in the release direction as the release air flow flows around the orifice.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.